That moment you realize you have nothing in common

My fiance and I have been together for 10 years. We have a 3 year old daughter together and he has a eleven year old daughter from a previous relationship. We have always had a good relationship even though we have nothing in common. He is not the kind of person who cheats or plays around he is here till the end kind of guy. I had met a girl through work a few months back and we have gotten along very well she infact actually lives with us 6 out of 7 days of the week due to her baby sitting out baby while we are at work. My friend has had a breakup a few short days after she and I had met (before she met my fiance).. and lost her job which it led me to being a good friend and helping her through the tough times and letting her stay here with us. While staying here I've realized more than ever I've always made jokes about it but it never stood out as much till now, but I came to realise that They have everything in common and it upseta me that they can sit and talk for hours about all kinds of stuff thatbi have no idea about. I just feel lost and afraid that he will be wanting more and ive juat became boring. Please any advice will help me out I just feel like the boring house wife